1. Field of the Invention
The present invention is directed to a catheter for drug delivery and, in particular, to a catheter for the delivery of a therapeutic agent into body tissue while reducing unwanted reflux.
2. Description of Related Art
Fluids or therapeutic agents may be delivered into various parts of the body that already contain a fluid or liquid such as epidurally or intrathecally into the spinal space. The delivery of a therapeutic agent into a fluid or liquid does not produce as much resistance or pressure as when dispensing directly into tissue. The fluid being dispensed from the catheter attempts to find the path of least pressure or resistance. In the case of tissue as the target of injection this path of least resistance or pressure often times causes the therapeutic agent to disadvantageously travel back up the catheter track defined as the space between the targeted tissue and outer surface of the catheter, otherwise referred to as reflux, back flow or leakage. Such back flow may result in catheter contamination or exposure of a larger area of the tissue to the therapeutic agent.
Convection enhanced delivery is the injection under positive pressure of fluid containing a therapeutic agent. This technology allows focused delivery of a therapeutic agent to a specific target area. Direct delivery is advantageous in that it reduces if not eliminates side effect complications that would otherwise arise from the delivery of a the therapeutic agent systemically. Another advantage is that convection enhanced delivery can increase the activity of the drug and deliver therapeutic concentrations not possible using conventional means. Therapeutic agents previously unable to reach a targeted tissue through oral delivery may now be reconsidered for direct delivery.
In brain tissue, drug formulations are difficult to develop due to the blood-brain barrier transport properties. Typically, molecules enter the cerebral spinal fluid or brain tissue in three ways: (i) by diffusion of lipid-soluble substances, (ii) by facilitative and energy-dependent receptor-mediated transport of specific water-soluble substances, and (iii) by ion channels. Protein based drugs do not typically fall into any of these three categories, and thus are usually not amenable to oral or intravenous delivery.
Recent study has focused on the direct infusion of proteins in the brain as a possible treatment of Parkinson's disease. In particular, the treatment of Parkinson's disease has recently concentrated on the delivery of the therapeutic agent directly into the grey matter brain tissue such as in the putamen. Conventional catheters permit backflow and reflux back up the catheter track that produces undesirable side effects if used to deliver proteins to the putamen.
U.S. Patent Publication No. 2007/0088295 discloses a step-design cannula and delivery system for chronic delivery of therapeutic substances into the brain using convention-enhanced delivery of therapeutic substances and which effectively prevents reflux in vivo and maximizes distribution into the brain. A delivery sheath is used for positioning the infusion cannula in the brain. The proximal end of the delivery sheath functions as the most external segment of the step-design of the infusion cannula, thereby increasing the overall number of steps in the step-design. Once the delivery sheath and cannula are placed at the proper depth, the assembly is fixed in position, for example, using an o-ring shaped holding bracket through which a bone screw is inserted to rigidly attach the holding bracket to the skull. After the assembly is positioned, only the upper portion of the delivery sheath is removed by cutting the sheath just above the points where the infusion cannula bends over leaving in place that portion of the delivery sheath implanted in the body. The system in accordance with the published patent application employs a delivery sheath as a guide because the central lumen is populated from the source to the distal tip with an infusion tube and thus a stylet cannot be directly inserted into the central lumen. The use of a delivery sheath while positioning the cannula in such a manner and leaving it implanted thereafter is disadvantageous in that it provides an allowance or opening between the proximal end of the delivery sheath and the distal catheter that is prone to reflux and back flow of the therapeutic substance thereby defeating the underlying purpose of the device. In addition, the published patented application catheter has a single exit port through the distal end of the catheter.
It is therefore desirable to develop an improved catheter design for delivery of a therapeutic agent directly into tissue that reduces or prevents reflux and back flow while eliminating the need for a guide or delivery sheath during positioning. Furthermore, an improved catheter is needed with an adjustable flow rate via multiple output ports.